Derwent Estuary-Bruny Surface Water Management Area is within Tasmania and is 1,104 km2
The Hobart water supply area is in the south east of Tasmania and for the purpose of the water balance is defined as the Derwent Estuary-Bruny surface water management area (1,104 km2). This excludes the majority of the physical Derwent water catchment which comprises the Upper and Lower Derwent River WMAs as well as the Derwent Estuary-Bruny WMA.
The Department of Primary Industries and Water (DPIW) is the licensing authority and manages both surface and groundwater diversions for urban, commercial/industrial, irrigation and environmental purposes. Hobart Water manages the major storages and protects the water quality in Hobart for bulk water supply. They also treat the bulk water and deliver it to local governments for distribution.
The majority of Hobart’s water supply comes from outside of the catchment. The supply network contains six major water storages within the WMA and a further two storages in the neighbouring Upper and Lower Derwent River WMAs. Within Derwent Estuary-Bruny, there are a number of creeks that drain into the estuary. The largest river totally contained within the WMA is the North West Bay River which flows from the south side of Mount Wellington to North West Bay (DPIWE, 2005a). The Derwent and Jordan Rivers both flow into and through the WMA but the majority of the water in these rivers is sourced from outside the WMA and are fed by runoff in the WMA. In the water balance the flows from the Derwent and Jordan Rivers are portrayed as a transfer in and out. The Derwent River itself is highly regulated downstream of Lake Meadowbank. The tidal limit in the Derwent River is about 1 km upstream of the New Norfolk Bridge in the Lower Derwent WMA.
Hobart Water supplies water from five major sources; just over half is drawn from the Derwent River from below Lake Meadowbank (operated by Hydro Tasmania), 15% from Lake Fenton, 20% from Hobart Mountain (Mount Wellington), 10% from the Southern Regional Supply and 2% from Glenorchy Mountain (Mount Arthur). This water is used to supply councils within the Hobart area and also to the Jordan and Pittwater-Coal water management areas and off-peak direct supply to the South East Irrigation Scheme. The supplies from Lake Meadowbank, Lake Fenton and the Southern Regional Supply constitute transfers into the WMA (Hobart Water, 2005). Hydro Tasmania release 20 cumecs from Lake Meadowbank; this release meets environmental requirements and the needs of Hobart Water at the Bryn Estyn treatment plant.
Figure 2 shows the major dams and the water supply distribution network within the Hobart water supply area.
Figure 1 Hobart water supply area locality map
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Hobart water supply area locality map (1.1 Meg)
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Figure 2 Hobart water supply area schematic map (Source: Hobart Water, 2006)
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